The current invention was designed to record the feeding processes of aphids and other soft-bodied, piercing-sucking agricultural pests. These insects spread numerous, deleterious plant viruses that cause many millions of dollars in damage to crops worldwide every year.
Aphids and other piercing-sucking insects acquire plant pathogens from infected plants and inoculate them to healthy plants. After aphids acquire the pathogens, it remains in the insect's body throughout its life. Researchers (including the inventors) are attempting to combat these plant diseases by better understanding how aphids and other vectors of plant pathogens carry and spread the pathogen via their feeding processes.
One means of studying the transmission of the disease is through an understanding of the way the insects feed. Direct current electrical penetration graph (EPG) technology provides information regarding the way that the insect draws its fluid food from plants. The EPG process is initiated by attaching a gold wire to the body of a sharpshooter and placing the sharpshooter in a feeding position on the leaf of a host plant. A plant electrode is then placed in the soil adjacent to the plant or attached directly to a part of the plant. A lead wire from the plant electrode and the gold wire attached to the insect are then connected to a monitoring device.
When the stylets (the probing and penetrating mouth parts of the insect) connect with the host plant, an electrical circuit is completed. As the insect's stylets probe the host plant, the voltage in the circuit fluctuates. The voltage fluctuations are depicted as waveform data on a computer monitor or on a time-based chart in a similar manner to an electrocardiogram (EKG) chart. Researchers have been able to correlate the waveform data (i.e. voltage fluctuations) with certain feeding activities to better understand the biological mechanisms that facilitate the spread of the Xylella fastidiosa bacteria.
Although the hardware associated with the direct current EPG monitoring process has been around since the 1970s, no meaningful update of the monitoring system design has apparently been attempted since its inception. The currently available monitor has been marketed under the name “Giga 8” or “Giga8”, although a cursory search of the US Patent and Trademark Office, Trademark Electronic Search System indicates that neither name is trademarked in the US.
The Giga 8 is a direct current EPG monitor that was originally designed primarily for aphids and other small piercing-sucking insects. Aphids are very tolerant of direct current excitation signals and consequently direct current EPG monitors continue to be used to study aphids. However, even for these direct current tolerant insects, the Giga 8 is no longer sufficiently suited for scientific inquiry. The direct current EPG system of the current invention eliminates several problems with the Giga 8, and also expands its usefulness for other, direct current-tolerant insects, especially larger insects such as large leafhoppers and heteropterans.
Among other things, the excitation voltage source of the Giga 8 is unregulated and uncompensated. The excitation control potentiometer has a negative DC voltage applied to one end of a fixed resistance element and a positive voltage applied to the other. Further, the excitation voltage cannot be precisely and reproducibly set. No means is available to determine the actual excitation voltage selected because the instrument is not capable of calibration. The excitation voltage is fed directly out from the control potentiometer wiper, without compensation to stabilize the voltage at any set level and the instrument has no index or dial settings available for reference and adjustment.
Although the Giga8 has a head stage amplifier (i.e. “head amp”), the head amp is limited to a single, fixed input resistance setting. This severely limits the sensitivity of the Giga 8, making it only useful for aphids and closely related insects. The main internal amplifier of the Giga 8 has a very low gain. This is not problematic for the small range of insect species that it was designed to monitor, but the Giga 8 design limits the instrument's ability to study other species of arthropod.
Further, as with other aspects of the Giga 8, the gain control has no scale. An operator simply arbitrarily adjusts the gain control until he/she is satisfied with the result. Consequently there is no means of documenting the exact instrument settings associated with the produced waveform data, therefore the results obtained from an evaluation using the Giga 8 are not precisely reproducible and verifiable by other researchers.
As indicated above, most of the electronic components of the Giga 8 are obsolete. For example, the Giga 8 operational amplifier is a μA741, which was designed in the 1970's. It has a very limited ability to change the output voltage to follow the input signal (i.e. slew rate). At even a moderate gain, the output may not closely resemble the shape of the input waveform, especially when the amplitude changes rapidly. Thus, output signals may be inaccurate and artifactual.
Because of the limitations described supra, the Giga 8 is only marginally useful. The need exists for a new EPG monitor that includes updated components as well as a wider range of applicability.
The current invention provides an EPG monitoring system that includes the ability to produce more detailed, accurate, and higher-resolution waveforms than the prior art system. The EPG monitoring system of the current invention also provides switchable amplifier sensitivities and expands the utility of the direct current EPG process to essentially all direct current-tolerant piercing-sucking arthropods.